// 1. let const
const a = 10;
let b = 20;
// 2.箭头函数

const fn = () => {
  let arr = [1,2,3,4,5];
  let res = arr.findIndex(item => item === 2);
  return res
};
fn()
console.log(a+b)
// 3. Array.isArray()  Object.keys()
export default fn;
